1. Field of the Invention
The invention relates in general to the method of display by sub-frame driving, and more particularly to the method of display on a monitor by sub-frame driving.
2. Description of the Related Art
With the improvement and innovation of science and technology, the development of display technology changes rapidly and makes progress at a tremendous pace. The traditional CRT (Cathode Ray Tube) display has gradually dropped out the display market due to its large volume and serious radiation and is gradually replaced by LCD (Liquid Crystal Display), OLED (Organic Light Emitter Diode), or PDP (Plasma Display Panel), which are thin and have low radiation, low power consumption.
The frame data input to the display has two parts—pixel data and display timings. A driving voltage is determined according to the pixel data, and then the brightness of a pixel is determined according to the driving voltage. In addition to the pixel data, the frame data include a set of display timings, which have three parameters. The three parameters are Hs (Horizontal Synchronal signal), Vs (Vertical Synchronal signal), and CK (pixel clock). CK (pixel clock) represents the number of the pixels per second, which determines the interval between the action of displaying colors of some pixel and that of the next pixel. When the pixel corresponding to the input pixel data is the last pixel in a row, Hs (Horizontal Synchronous signal) controls to display the first pixel in the next row. Therefore, Hs (Horizontal Synchronous signal) determines the number of the rows per second. When the pixel corresponding to the input pixel data is the pixel of the last column of the last row in the screen, Vs (Vertical Synchronous signal) controls to display the first pixel of the first row. Therefore, Vs (Vertical Synchronous signal) determines the number of the displayed frames per second.
Take an LCD monitor for example. The transparency of each pixel is changed according to the driving voltage Vd applied, and accordingly the brightness of the pixel is determined. According to the pixel data, a target driving voltage VD is determined to let the pixel achieve a target transparency TD. When the driving voltage Vd rises to the target driving voltage VD, the transparency of the pixel cannot achieve the target transparency TD in real time due to the slow response of the liquid crystal in the pixel of the LCD monitor. FIG. 1A is a diagram of the driving voltage Vd of the pixel (i,j) vs. time. Pixel (i,j) is one of the pixels in the LCD monitor. The driving voltage Vd reaches the target driving voltage VD in a short time. FIG. 1B is a diagram of the transparency of the pixel (i,j) vs. time. When the driving voltage Vd is applied to the pixel (i,j), the transparency of the pixel (i,j) rises accordingly. But the transparency of the pixel (i,j) takes a longer period t1 to reach the target transparency TD.
A well-known method to speed up the response of the liquid crystal is to apply an over-drive voltage Vo, which is higher in magnitude than the desired target driving voltage VD. FIG. 2A is a diagram of the driving voltage Vd vs. time using the over-drive method. First, the driving voltage Vd rises to the over-drive voltage Vo for speeding up the response of the liquid crystal in pixel (i,j). FIG. 2B is a diagram of the transparency of the pixel (i,j) vs. time according to the driving voltage Vd shown in FIG. 2A. The transparency of the pixel (i,j) reaches the target transparency TD faster than that shown in FIG. 1B.
However, it is not easy to control the magnitude of the over-drive voltage Vo. If the over-drive voltage Vo is too high, the transparency may exceed the target transparency TD; if the over-drive voltage Vo is too low, the response of the liquid crystal may not be fast enough.